Peter wrote:
MikeMl wrote

If it detects what it thinks is an "overvoltage" condition,
then it responds by firing its "protection crowbar", which instantly
overloads the aircraft's Field Breaker, causing it to overheat and trip,
which removes power from the LR3C, and therefore removes excitation from
the Alternator's field circuit, thereby taking the entire charging
system offline until the Field Breaker is reset.

I personally think this is a DUMB design that causes many more problems
than it prevents.

I am an electronics engineer (35 years' design experience) and can't
believe anybody would do something so stupid in an aeroplane.

Overvoltage crowbars are used on switching power supplies which have
instant acting short circuit protection features and whose output
power is limited by the magnetic components anyway.

But on an aeroplane you have a very powerful alternator and more to
the point you have thermal circuit breakers which take a while to
trip. They are not like the magnetic ones in one's house which trip
really fast. The thermal ones have to heat up first.

If one was going to do an overvoltage protector for an aeroplane, the
way to do it is to put something in series with the alternator field
winding (i.e. in series with the existing voltage regulator) which
goes open circuit when the bus voltage reaches say 32V. That will kill
the alternator output very fast.

I think the problem with that approach is that the
huge inductive surge of the field collapsing would
add to the already present overvoltage.

Crowbars are used in military and spacecraft design
where a positive zero-volts shutdown is needed.